For three days this week, Washington, D.C., was riveted as the three branches of government faced off dramatically in a packed room on First Street Northeast, and when it was all over, President Barack Obama’s health care law was hanging by a thread.

Dozens of Members of Congress attended at least one of the three days of oral arguments before the Supreme Court, including the principal authors of the law and its chief opponents. Attorney General Eric Holder, Health and Human Services Secretary Kathleen Sebelius and top White House aide Valerie Jarrett were among those representing the White House.

They sat quietly, without even a cellphone, momentarily powerless amid hundreds of others in the crowded chamber and just feet in front of the nine people who would decide the fate of a law with almost unprecedented legal and political stakes.

It was a marked contrast to the circus-like atmosphere just outside the court, with nonstop protests, for and against, and rolling press conferences conveniently staged on the Capitol lawn with the court building in the background. Politicians and activists mugged for cameras, a small brass band passed by at one point, and even presidential candidate Rick Santorum rolled up in his motorcade to take advantage of the spotlight.

For opponents of the law, no less than freedom itself is on the line. If Congress has the power to compel people to buy health insurance, what could it not do?

For supporters, the health of more than 40 million without insurance is at stake, as well as the power of Congress to take actions to deal with major national problems.

Indeed, the questions raised by this week’s oral arguments moved beyond health care and into the limits of the government.

Would the court begin to roll back more than 70 years of expanded government powers dating to the New Deal — powers that led to Social Security, Medicare, Medicaid and environmental laws? Would it toss aside merely the heart of the law — a mandate to buy health insurance — or invalidate the whole thing? And would it push back against the federal government’s ability to use the power of the purse to spur states to take actions that they otherwise would not support?

Energy and Commerce Chairman Fred Upton (R-Mich.), after attending his first court argument Wednesday, hesitated to make a guess. “It’s a lot like filling out your brackets,” he joked, referring to the ongoing March Madness college basketball tournament.

But Upton noted that the court on Wednesday was repeatedly asking what Congress’ intent was — even as Members were sitting in the audience.